Reliable information on chemical equilibria in formaldehyde solutions is needed for the design of separation process for formaldehyde containing mixtures. Chemical equilibria of the poly(oxymethylene) glycol formation in formaldehyde solutions in water (and deuterium oxide) and of the poly(oxymethylene) hemiformal formation in methanolic formaldehyde solutions were studied by H-1- and C-13-NMR spectroscopy. Overall formaldehyde mole fraction and temperature range from 0.06-0.19 mol/mol, 275-357 K for solutions in water and 0.17-0.50 mol/mol, 274-317 K for methanolic solutions. Chemical equilibrium constants are determined assuming ideal solution behavior. Results from H-1- and C-13-NMR spectroscopy agree well. Chemical equilibria of the poly(oxymethylene) glycol formation do not depend on whether water or deuterium oxide is used. The new experimental results confirm only some of the literature data.